1. Technical Field
Embodiments of the present invention relate to a light guide plate for a back light unit of a liquid crystal display (hereinafter, referred to simply as a “LCD”) device. More specifically, embodiments of the present invention relate to a light guide plate for an LCD back light unit, wherein the light guide plate has a rear surface formed with a main prism portion including a plurality of prisms, and a front surface formed with a front-lens part including a plurality of optical members such as lenticular lenses or microlenses, so as to improve visibility of a predetermined pattern of the main prism part.
2. Background Art
In general, an LCD device refers to a device which displays numerals or images through application of an electric field to liquid crystals disposed between two glass substrates, in which the liquid crystals are made of a material having an intermediate phase between a liquid and a solid.
Since the LCD device is not a self-luminescent device, it must be provided with a back light unit as a light source to generate light. An image is displayed in such a manner that transmittance of light generated from the back light unit is adjusted in a liquid crystal panel, in which liquid crystals are uniformly arranged.
According to a position of a light source that emits light, an LCD back light unit is classified to a direct-type back light unit in which the light source is directly positioned at a rear side of a liquid crystal panel of LCD, and an edge-type back light unit in which the light source is positioned at a side of the liquid crystal panel of LCD. According to a shape of a light guide plate, the edge-type back light unit is sub-classified to a wedge-type back light unit and a flat-type back light unit.
FIG. 8 is a view illustrating the structure of a conventional back light unit using a wedge-type light guide plate.
A light source 2 serves to emanate light initially in the LCD device. Although various types of light source can be used, the LCD device generally employs a cold cathode fluorescence lamp (CCFL) which involves low power consumption and emits highly bright white light.
A light guide plate 4 is provided below the rear side of an LCD panel and at one side of the light source 2 and serves to convert spot light generated from the light source 2 into plane light and thus project the plane light forward to the LCD panel.
A reflection plate 3 is arranged on a rear side of the light guide plate 4, and serves to reflect light emitted from the light source 2 toward the LCD panel disposed in front of the reflection plate 3.
The diffusion sheet 5 is arranged on a front side of the light guide plate 4, and serves to make uniform light passing through the light guide plate 4.
While the light passes through the diffusion sheet 5, diffusion of light occurs in horizontal and vertical directions so that brightness is rapidly deteriorated. In this regard, prism sheets 6 are used to reflect and concentrate the light, thereby providing enhanced brightness.
A protective sheet 7 is arranged above the prism sheets 6, and serves to prevent scratches on the prism sheet 6, and to prevent Moire effect from occurring when using the prism sheets 6 arranged in two layers in the horizontal and vertical directions.
The back light unit further includes a mold frame (housing) that serves as a case to allow respective components of the back light unit to be fixed so that the back light unit can be integrated, and a lamp cover (back cover) to protect the back light unit while serving to maintain the strength of the back light unit and support the back light unit.
As shown in FIG. 8, the light source 2 is generally located at one edge of the back light unit (for an LCD TV, the light source is often located directly at the rear side of a panel). As a result, light is not uniformly transmitted through the overall surface of the unit, so that the edge of the back light unit can be brighter than any other portions of the back light unit. In order to prevent this phenomenon, the light guide plate 4 is used. The light guide plate is generally made of a transparent acrylic resin, which is not easily breakable due to its high strength, and has deformation resistance, light weight and high transmittance of visible light.
In other words, the light guide plate 4 serves to allow light emitted from the light source 2 to be uniformly projected to the overall surface of the light guide plate 4. In practice, however, in a case where the back light unit is disassembled and light is allowed to emit from the light source 2 located at one side of the light guide plate 4, the light is not uniformly projected to the overall surface of the light guide plate 4, but is concentrated on both ends of the light guide plate 4. This is because the light guide plate 4 guides the light from the light source 2 to the opposite side of the light guide plate 4.
Thus, the rear surface of the light guide plate 4 is subjected to a specific treatment to cause scattered reflection of light in the light guide plate 4 such that light can be transmitted through the overall surface of the light guide plate 4. Specifically, the rear surface of the light guide plate 4 is formed with a prominence/depression pattern which has a predetermined shape designed in consideration of a distance from the light source 2 and the like. When the prominence/depression pattern is formed on the rear surface of the light guide plate 4, plane light having higher brightness and uniformity is emitted through the overall surface of the light guide panel of the LCD device.
However, in the conventional LCD device constructed as above, a portion of the panel with the prominence/depression pattern formed therebelow looks bright, and the other portions of the panel without having the prominence/depression pattern therebelow looks dark, so that there occurs a spot phenomenon on the panel, thereby deteriorating the visibility of the LCD device. In particular, as the LCD panel is increased in size, a region separated a far distance from the light source 2 lacks in absolute amount of light reaching there, and looks dark.
In addition, the diffusion sheet and the prism sheets are used for improvement of light uniformity, and cause an increase in manufacturing costs of the back light unit.
In order to solve the above problems, there is a need for a great deal more research to obtain plane light with excellent visibility, high brightness and good uniformity over the entire surface of the LCD panel without using the diffusion sheet or the prism sheets.